Thin electrically conducting films of gold are bonded to non-electrical conducting oxides such as alumina to form what is commonly referred to as microstrip boards. These boards find use in conducting high frequency electrical energy of microwaves and in a number of other applications.
However, it is fairly difficult to attach a thin film of gold to non-conducting oxides such as alumina. The current practice with alumina, for example, is to evaporate a thin film of chromium followed by the evaporation of gold. The substrate's temperature must be controlled at high values during the evaporation to effect a good oxide-chromium bond and to properly form an alloying type of bond between the chromium and gold. Although the resulting metalization is an electrical conductor, adheres well and is suitable for conventional chemical milling procedures providing that each metal involved be etched separately, this process suffers from a number of disadvantages. Thus great care must be taken to apply a layer of chromium sufficiently thick for bonding the gold but not so thick that the electrical resistance of the film is affected by the chromium. Furthermore, the two-step process involved in etching the desired pattern is cumbersome and requires the expense of using two different solutions. With respect to expense, it should also be noted that at times chromium becomes rather scarce and hence it can be very expensive. Additionally, control of the substrate temperature during evaporation is difficult and the chromium-gold interfacial alloy is difficult to etch.
In view of these difficulties, research has been conducted to find easier ways to bond gold films to non-electrical conducting oxides.